The present invention is directed to bicycle transmissions and, more particularly, to an adjustable bicycle derailleur.
Bicycle derailleurs typically comprise a base member mounted to the bicycle frame and a movable member coupled for moving relative to the base member. The movable member supports a chain guide that moves a drive chain among a plurality of drive sprockets, and an actuating arm normally controls the movement of the movable member. A return spring biases the movable member and the actuating arm toward respective home positions. A control wire normally is attached to the actuating arm such that pulling the control wire causes the actuating arm and the movable member to move away from their respective home positions against the biasing force of the return spring. Likewise, releasing the control wire causes the actuating arm and the movable member to move toward their respective home positions as a result of the biasing force of the return spring.
The actuating arm typically has the shape of a lever. Thus, as the rotational angle of the actuating arm changes, the angle between the control wire and the actuating arm likewise changes. This, in turn, causes a variation in the amount of force required to pull the actuating arm. Very often the angle between the actuating arm and the control wire becomes more obtuse as the control wire is pulled, thus decreasing the component of the pulling force in the rotational direction of the actuating arm. Since the resistance of the return spring increases as the actuating arm moves progressively away from the home position, the amount of pulling force that the rider must exert on the control wire can become significant. Also, such an increased pulling force tends to fatigue the control wire and the actuating arm, thus increasing the risk of failure of both components. One solution to this problem is to design the home position of the actuating arm to maximize the mechanical advantage of the control wire throughout the range of motion of the actuating arm. Such a solution is shown in U.S. Pat. No. 5,496,222.
Another consideration in derailleur operation is the actuation ratio, which is the amount of movement of the chain guide per unit of movement of the control wire. The actuation ratio can change depending upon the rotational position of the actuating arm. As a result, a rider operating a derailleur with an actuating arm in the form of a simple lever must pull the control wire by different amounts to shift from one gear to another. A solution to this problem, shown in U.S. Pat. Nos. 5,496,222 and 5,533,937, is to have the control wire wrap around a variable-radius winding surface to compensate for the variations in the actuation ratio.
Different derailleurs have different actuation ratios and lever arm configurations, and the position of the derailleur relative to the control wire can be different for different bicycles. Thus, in order to fully compensate for changing mechanical advantages and actuation ratios, a derailleur would have to be designed for each possible bicycle configuration.
The present invention is directed to an adjustable bicycle derailleur wherein the mechanical advantage and/or the actuation ratio may be adjusted as required for the particular application. According to the present invention, not to be limited thereto, a derailleur includes a base member, a movable member coupled for moving relative to the base member and supporting a chain guide, a first actuating unit for moving the movable member relative to the base member, and a second actuating unit for moving the first actuating unit. In one embodiment, the second actuating unit includes a wire winding surface, and a position adjuster is provided for adjusting a relative position between the first actuating unit and the second actuating unit. In another embodiment, the second actuating unit comprises a first actuating member movably coupled to a second actuating member, and a position adjuster is provided for adjusting a relative position between the first actuating unit and the second actuating unit. Alternatively, a position adjuster is provided for adjusting a relative position between the first actuating member and the second actuating member.